Investments (Narrative) (Details) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
Dec. 31, 2013	Dec. 31, 2012
Investment [Line Items]
Fixed maturity securities - available for sale, at market value	$ 5,201,921	$ 5,531,410
Percentage threshold that triggers a review of available for sale debt securities for declines in market value	80.00%
Aggregate market value of investments in unrealized loss position	1,657,025	630,658
Gross unrealized losses on investments in unrealized loss position	64,557	20,305
Percentage threshold of unrealized losses not exceeded by any one single issuer	0.90%	0.20%
Fixed maturity securities, duration of unrealized loss, less than 12 months, gross unrealized depreciation	44,868	4,642
Fixed maturity securities, duration of unrealized loss, greater than 12 months, gross unrealized depreciation	19,687	15,661
Additional contractual commitments	55,171
Other invested assets, at fair value, shares	9,719,971
Percentage of shares representing the total outstanding shares	17.00%
Securities with a carrying value	1,405,722
Minimum [Member]
Investment [Line Items]
Limited partnership financial reporting lag time, months	1 month
Maximum [Member]
Investment [Line Items]
Limited partnership financial reporting lag time, months	3 months
Foreign Government Securities [Member]
Investment [Line Items]
Fixed maturity securities - available for sale, at market value	674,827
Aggregate market value of investments in unrealized loss position	130,158	48,313
Gross unrealized losses on investments in unrealized loss position	7,941	3,735
European Sovereign Securities [Member]
Investment [Line Items]
Fixed maturity securities - available for sale, at market value	88,660
Percentage threshold maximum of securities held in sovereign debt	5.00%
France [Member]
Investment [Line Items]
Percentage of securities held in sovereign debt of a specific country	53.00%
United Kingdom [Member]
Investment [Line Items]
Percentage of securities held in sovereign debt of a specific country	14.20%
Sweden [member]
Investment [Line Items]
Percentage of securities held in sovereign debt of a specific country	13.70%
Netherlands [Member]
Investment [Line Items]
Percentage of securities held in sovereign debt of a specific country	7.40%
Investment Grade [Member]
Investment [Line Items]
Fixed maturity securities, duration of unrealized loss, less than 12 months, gross unrealized depreciation	38,527	3,281
Fixed maturity securities, duration of unrealized loss, greater than 12 months, gross unrealized depreciation	18,867	14,401
Sub-Prime And Alt-A Loans [Member]
Investment [Line Items]
Fixed maturity securities, duration of unrealized loss, greater than 12 months, gross unrealized depreciation	$ 33	$ 33

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Investments in notes or bonds that are collateralized by a specific group of underlying assets owned by the issuer of the notes or bonds which are short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three-years ago does not become a cash equivalent when its remaining maturity is three months.

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